“I’m disappointed and at the same time sad, but what can I do?” she said.

The decision brings a conclusion to what authorities and school officials called a highly delicate and unusual case, given the ages of the victim and possible suspect.

“This case was a fight between two children that ended with unintended and tragic results,” Long Beach police said in a statement. The department “hopes that its conclusion brings some peace to both families involved, as well as the community.”

Authorities said Joanna died Feb. 24 of blunt-force trauma to the head after a pre-planned fight with an 11-year-old classmate in an alley near Willard Elementary School. Some relatives believed the girls were fighting over a boy.

Joanna fell ill after the fight, which lasted about a minute, and died hours later. Her death was later ruled a homicide by the Los Angeles County coroner’s office. No arrests were made during the investigation, which has now been closed.

Jane Robison, a spokeswoman for the district attorney’s office, acknowledged the decision, but declined to speak further about it because the case involved two juveniles. Prosecutors reviewed the case for just over a month before making their decision.

Villanueva said she plans to speak to her attorney about other options. If nothing can be done, she said, “it’s over and we leave it in peace.”

Villanueva said she feels sorry for the 11-year-old girl who fought her daughter: “I think she won’t be happy in her life knowing that she killed someone.”

Joanna, who died a couple weeks shy of her 11th birthday, liked to sing and hoped one day to be as famous as Selena, the late Tejano music sensation. The fifth-grader enjoyed watching “Glee” and telenovelas and she was remembered by her mother at a memorial service at Hollywood Forever Cemetery as a “good and happy little girl who dreamed of being a singer and a star.”